Reports of drug-induced flashbacks have existed since the 1950s. Though the term "flashback" wasn't used specifically until 1969, as early as 1954 scientists noticed LSD users complaining of a reoccurrence of an LSD-like state long after the drug's effects should have worn off.

The risk of a flashback has become a standard line in anti-drug messaging. Months or years after taking LSD, suddenly, the trip could come back without warning, and suddenly you would be floridly hallucinating again. An urban legend holds that molecules of LSD stay in the body, hiding in fat or in the spine, and can later be re-released.